The invention relates to an ultrasonic filling level sensor having an elongated measuring chamber, which is provided with an opening at each of its two ends and in which a liquid has the same filling level as outside the measuring chamber, and having an ultrasonic transceiver, which is associated with one end of the measuring chamber and the emitted sound signals of which are reflected at the surface of the liquid and at a calibrating reflector and received by the ultrasonic transceiver, in order to determine the filling level from the relationship between the transit times of the two signals.
An ultrasonic filling level sensor is disclosed by DE 4328046 Al. This document describes a device forming a tube which is coated on the inside and in which a rod is to be disposed. Located at the bottom of the tube is an ultrasonic transceiver. This emits an ultrasonic signal, which travels along the direction of the extent of the tube or of the rod disposed in it, is reflected at the surface of the liquid and received by the ultrasonic transceiver. At a defined distance from the bottom, that is from the transceiver, there is a calibrating reflector. The liquid level can be determined from the relationship between the transit time of a signal reflected there and the signal reflected at the surface of the liquid. As a result of the rod disposed in the tube, the liquid sensor described there is intended to be capable of also operating in the tilted state.
DE 33 30 059 C2 describes a liquid sensor in a tank, with which an ultrasonic signal is passed through a hollow line, having an irregular form, to be reflected at the surface of a liquid.
DE 43 076 35 A1 discloses a filling level measuring device which is provided with a large number of reflectors. The height of the liquid is calculated from the relationship between the difference between the arrival times of the pulses from the two uppermost submerged reflectors and the difference between the arrival times of the pulses from the surface of the liquid and the uppermost submerged reflector.
DE 44 194 62 C2 describes a liquid sensor in the form of a dipstick. The liquid sensor can be inserted into the opening of a tank. The dipstick can thereby be inserted through the opening of a ball valve. The signal emitted by an ultrasonic sensor is reflected at a float.
DE 33 30 063 C2 discloses a liquid level gage for irregularly shaped liquid containers of vehicles. Also provided here is an evaluation device, which determines the number of not submerged reference reflectors and the number of submerged reference reflectors.
Also known from the prior art, for example DE 40 253 26 C2, are liquid sensors with which a separate measuring chamber is not used. Rather, the sound signal is emitted directly from the bottom of the container. To ensure that the sound signal is reflected at a reflection area of the surface directed toward the ultrasonic transceiver, an acoustic lens is provided there.
When elongated, in particular tubular, measuring chambers are used, the sound waves are emitted by a transceiver disposed at the bottom of the measuring chamber. They pass through the elongated measuring chamber substantially without being reflected at the walls of the measuring chamber, to be reflected at the surface of the liquid. Only the portion of the reflected sound signals that is reflected precisely in its direction reaches the transceiver. Such a filling level sensor only functions when the reflection area is directed toward the ultrasonic transceiver, that is to say extends substantially transversely to the longitudinal direction of the measuring chamber. For this reason, the known ultrasonic filling level sensors can substantially only be used in a vertical position. In the case of the aforementioned, generically determinative DE 4328046 A1, a rod is intended to make it possible for the sensor also to be used at great tilting angles with respect to the vertical. A device of this type is complex and cannot be used as a dipstick.
The invention is therefore based on the object of developing an ultrasonic filling level sensor of the generic type which is simpler in terms of production engineering and advantageous in use.